Objective: The purpose of this study was TLP bonding of IN-738LC nickel based superalloy components used in turbine industry using BNi2 and MBF-15 amorphous foils produced in materials research center of ACECR. Determination of optimum process conditions of bonding and comparison of the microstructure and shear strength of bonded joint area with similar results presented in the papers was the second goal of the study.
Experimental procedure: In this research, the TLP brazing process and characterization experiments were carried out according to AWS B2.2 standard. The bonding process was done at predetermined temperature range, based on DTA results of the foils, for specified times under vacuum atmosphere. The microstructure evolution and shear strength of the bonded joint were investigated by alternation of TLP process parameters including brazing temperature, time and the foil thickness, and the optimum conditions of the process were determined. Some of the bonded samples were sent to the laboratory of Taiwan national university for further investigation and the results were compared.
Results: The examination of microstructural results indicated that the bonded area can be consisted of three distinct regions of ASZ, ISZ and DAZ, considering the brazing conditions. The microstructure of isothermally solidified zone (ISZ) is γ solid solution single phase and non-isothermally solidified zone (ASZ) consisted of eutectic phases, nickel and chromium rich borides and fine dispersoids of nickel silicide. Boride and carboboride phases enriched in chromium, having cubic or needle-like shape, were observed in diffusion affected zone (DAZ). The optimum bonding conditions were determined as the brazing at 1055oC for 30 min and at 1130oC for 30 min for BNi2 and MBF-15 foils, respectively. Comparison of the microstructure and shear strength properties of the samples brazed using BNi2 and MBF-15 foils produced in ACECR with the results reported in the literatures, indicated similarity of the properties.